Traffic lights are routinely used to control traffic along roadways and intersections. These traffic lights are often required to be powered by line voltage supplied by overhead wires. These traffic lights, while individually not requiring substantial amounts of power to illuminate the individual traffic signals, in total relatively large amounts of electrical power is used in the illumination of the traffic lights. Recently, there has been much development in traffic lights utilizing light emitting diodes rather than other forms of incandescent illumination. While the light emitting diodes are relatively efficient and have a relatively long life, during daylight hours it is often difficult for a light emitting diode to generate sufficient illumination to be clearly visible. There have been many efforts to aid in making more visible the illumination from a traffic signal utilizing light emitting diodes.
One such light emitting diode signal light is disclosed in U.S. Pat. No. 6,599,002 issuing to Hsieh et al on Jul. 29, 2003 and entitled “LED Signal Light”. Therein disclosed is a light emitting diode signal light using a plurality of lens cells. The plurality of lens cells is used to redistribute the light in vertical and horizontal directions and adjust orientation of light to the specified illumination areas.
Another effort to enhance light emitting diode illumination, which may be used in a traffic light, is disclosed in U.S. Pat. No. 5,174,649 issuing to Alston on Dec. 29, 1992 and entitled “LED Lamp Including Refractive Lens Element”. Therein disclosed are a plurality of facets that allow a large area on the lamp to appear to viewers to be uniformly illuminated.
In addition to the problems associated with the use of LED lights, there is also a problem of power interruptions or reduced line voltage which reduces the light emitting diode output. One solution to reduced light emitting diode illumination caused by interruptions in line voltage is disclosed in U.S. Pat. No. 5,457,450 issuing to Deese et al on Oct. 10, 1995 and entitled “LED Traffic Signal Light With Automatic Low-Line Voltage Compensating Circuit”. Therein disclosed is a traffic light or signal using LED lights with a voltage compensating circuit that disables or re-engages a first and then a second set of LEDs in a traffic light as the input power voltage drops below a first and then a second threshold voltage. This results in the remaining LEDs being driven by an increased current, resulting in a greater light intensity.
While these prior patents disclose enhancements to LED traffic lights, there is a continuing need to improve LED traffic lights so as to be more visible and to conserve power. Additionally, there is a strong safety concern to develop a signal light that can function even during interruptions in line voltage or power.